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Articles 1 - 10 of 10
Full-Text Articles in Physics
Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces With Variable Acceleration, John D. Ramshaw
Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces With Variable Acceleration, John D. Ramshaw
Physics Faculty Publications and Presentations
A simple model is described for predicting the time evolution of the half-width h of a mixing layer between two initially separated immiscible fluids of different density subjected to an arbitrary time-dependent variable acceleration history a(t). The model is based on a heuristic expression for the kinetic energy per unit area of the mixing layer. This expression is based on that for the kinetic energy of a linearly perturbed interface, but with a dynamically renormalized wavelength which becomes proportional to h in the nonlinear regime. An equation of motion for h is then derived from Lagrange's equations. This model reproduces …
Factors Affecting Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan
Factors Affecting Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan
Physics Faculty Publications and Presentations
Methane emissions from rice fields are affected by a number of environmental and agricultural factors. We have analyzed our 7-year data set on methane emissions from rice fields in Tu Zu, China, to delineate the relationships between emissions and a number of variables that were measured at the same time. Our work was done in fields that were managed under prevailing agricultural practices of the region. Consequently, only the effect of factors that vary from year to year or during the growing season can be calculated. In our study we measured the effects of environmental variables (soil temperature, wind speed, …
Flux Measurements And Sampling Strategies: Applications To Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer
Flux Measurements And Sampling Strategies: Applications To Methane Emissions From Rice Fields, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer
Physics Faculty Publications and Presentations
The emissions of methane from rice fields and other sources are often measured by placing chambers on the surface and taking sequential samples. Although static chambers pose several problems that affect the accuracy of the data, there are a few parameters that, if carefully chosen, can improve the reliability of the data and reduce the uncertainties. These parameters are the length of time the chamber is kept on the rice plants, the number of samples that are drawn to estimate the flux, the basal area and height of the chamber, the frequency of measurements during the growing season, and the …
Effects Of Production And Oxidation Processes On Methane Emissions From Rice Fields, M. Khalil, R. A. Rasmussen, Martha J. Shearer
Effects Of Production And Oxidation Processes On Methane Emissions From Rice Fields, M. Khalil, R. A. Rasmussen, Martha J. Shearer
Physics Faculty Publications and Presentations
The emission of methane from rice fields is the difference between the amount produced in the anaerobic zone below the soil and the amount oxidized in the root zone. Plants can also contribute to methane production by exuding organic compounds that may be utilized by methanogenic bacteria. We measured methane emissions from rice fields at Tu Zu in China between 1988 and 1994, which gave average emissions of about 30 mg m⁻² h⁻¹. We estimate that 45-60% of the methane produced was oxidized before reaching the atmosphere; and root exudates may have contributed of the order of 10% of the …
Measurements Of Methane Emissions From Rice Fields In China, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan
Measurements Of Methane Emissions From Rice Fields In China, M. A. K. Khalil, R. A. Rasmussen, Martha J. Shearer, R. W. Dalluge, Lixin Ren, Chang-Lin Duan
Physics Faculty Publications and Presentations
Rice fields have always been regarded as one of the largest anthropogenic sources of atmospheric methane. Here we report the results of a 7-year study of methane emissions from rice fields in the Sichuan Province of China. In this region, there is one crop of rice per year, the fields are continuously flooded from transplanting to harvest, and there is heavy use of organic fertilizers. Emissions over the entire growing season were measured from each of up to 24 plots. Environmental variables were measured and relevant supporting data on the agricultural practices were recorded. The fields were studied under prevailing …
A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen
A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen
Physics Faculty Publications and Presentations
The Green dyadic formulation for calculating classical decay rates of admolecules at multiple planar interfaces first published by Chance, Prock and Silbey is reexamined. It is pointed out that, for the case of fluorescing molecules sandwiched between a system of super- and substrate interfaces, the original formalism requires significant modifications in order to lead to results consistent with those obtained from the Sommerfeld radiation theory.
Path Integral For The Quantum Harmonic Oscillator Using Elementary Methods, Scott M. Cohen
Path Integral For The Quantum Harmonic Oscillator Using Elementary Methods, Scott M. Cohen
Physics Faculty Publications and Presentations
We present a purely analytical method to calculate the propagator for the quantum harmonic oscillator using Feynman’s path integral. Though the details of the calculation are involved, the general approach uses only matrix diagonalization and well-known integrals, techniques which an advanced undergraduate should understand. The full propagator, including both the prefactor and the classical action, is obtained from a single calculation which involves the exact diagonalization of the discretized action for the system.
General Formulation Of The Semirelativistic Approach To Atomic Sum Rules, P.T. Leung, Scott M. Cohen
General Formulation Of The Semirelativistic Approach To Atomic Sum Rules, P.T. Leung, Scott M. Cohen
Physics Faculty Publications and Presentations
A general scheme is presented for obtaining systematic relativistic corrections to quantum-mechanical sum rules for various calculations in atomic physics. The single-particle picture and the Foldy-Wouthuysen transformation [Phys. Rev. 78, 29 (1950)] are adopted to derive such corrections. Results are obtained for the ldquogeneralized Bethe sums,rdquo which include all higher moments of the energy transfer, and explicit results are given to the lowest order of relativistic corrections.
The Surface Plasmon Enhancement Effect On Adsorbed Molecules At Elevated Temperatures, P.T. Leung, Hai-Pang Chiang, W. S. Tse
The Surface Plasmon Enhancement Effect On Adsorbed Molecules At Elevated Temperatures, P.T. Leung, Hai-Pang Chiang, W. S. Tse
Physics Faculty Publications and Presentations
The surface plasmon enhancement effect on adsorbed molecules at elevated substrate temperatures is studied theoretically using surface enhanced Raman scattering (SERS) as an example. The surface structure is idealized to be a monodisperse spherical particle with its nonlocal dielectric response accounted for. The temperature effects are modeled using a temperature-dependent collision frequency in the Drude model. Numerical results show that only a small decrease in the SERS enhancement ratio occurs for temperatures up to the melting point of the substrate, even for scattering close to the surface plasmon resonance frequency of the metal. More definitive results are subjected to more …
Self-Consistent Effective Binary Interaction Approximation For Strongly Coupled Multifluid Dynamics, John D. Ramshaw
Self-Consistent Effective Binary Interaction Approximation For Strongly Coupled Multifluid Dynamics, John D. Ramshaw
Physics Faculty Publications and Presentations
An improved self-consistent effective binary diffusion approximation for multicomponent diffusion was recently described [1]. Here we develop an analogous self-consistent effective binary interaction (SCEBI) approximation for simplifying multifluid dynamical descriptions in which each fluid is strongly coupled to the other fluids by pairwise frictional forces. The net drag force on each fluid is the summation of the drag forces due to each of the other fluids. This summation is approximated by a single term proportional to the velocity of the fluid in question relative to an appropriately weighted average velocity. This approximation permits an explicit numerical solution for the fluid …